Periodic Reporting for period 2 - MORE-TEM (MOmentum and position REsolved mapping Transmission Electron energy loss Microscope)
Période du rapport: 2022-11-01 au 2024-04-30
A major mission of condensed-matter physics is to understand material properties via the knowledge of the energy vs. momentum (q) dispersion and lifetime of fundamental excitations. Unfortunately, none of the available techniques can be applied to emerging nanomaterials: inelastic x-ray scattering & electron energy loss spectroscopy (EELS) in reflection lack the spatial resolution whereas EELS in transmission electron microscopy lacks the needed combined spatial, energy & q-resolution. In MORE-TEM, we develop a new spectrometer enabling to map excitations q-resolved with 0.01 Å-1 resolution and q-averaged down to atomic level, at unprecedented 1 meV energy resolution and at variable temperature between 700 K and 4 K. This breakthrough is possible by bringing together our synergy group with complementary skills in electron microscopy, electron optics, experimental & theoretical spectroscopy. This opens the so-far unexplored possibility to investigate dispersion and lifetime of phonons, plasmons & excitons in nanomaterials including (organic) molecules, 1D nanotubes, 2D materials, heterostructures & nanocrystals in minerals with a few nm of lateral resolution on samples as thin as an atomic monolayer. Mapping out the spatial and q-landscape of primary excitations will allow us to gain control on quantum phases, like charge-density waves and superconductivity, to engineer new materials for energy (e.g. batteries), (opto-)electronic devices in (organic) electronics, and to model the physical and chemical properties of natural geological systems. This will hugely impact a wide range of applications in physics, chemistry, engineering, as well as in environmental-, geo- & material science. MORE-TEM not only implements features of a large scale facility on a cheaper table-top instrument, but it also pushes q-resolved spectroscopy to the realm of the nanoscale, providing thus a fundamentally new & unique infrastructure for the characterization and optimization of nanomaterials.
Within the first year we decided on the optimal development platform for MORE-TEM. The selected JEOL platform combines both downward compatibility to the reference systems in Japan and upward compatibility for monochromator (MC) and spectrometer developments at CEOS and will be delivered next year. In the meantime, these reference TEMs 3C2 and 3C3 in Japan have been used for the project. We also worked on optimising reference setups for in-situ laser annealing inside a microscope cryostat as a prototype for MORE-TEM. CEOS started the production of a spectrometer and development of the monochromator. For this purpose CEOS decided to purchase an almost new JIG microscope by investing internal in-kind money which is already installed at CEOS premises and a specific novel MC design which has a different ray-path of the electrons from the known-configuration was designed. With this, the optical element’s exact optical properties are scanned and fitted to subsequently refine the full ray-path model of the MC. The ideal optical state, the robustness against misalignment and external disturbances are also optimised. This design was now introduced in [1]. Within the first two years of the project we worked on the theory side to describe, model and analyse the charge excitations (plasmon-phonon- and excitons) that can be measured by EELS spectroscopy, once MORE-TEM will reach its final performance. We discovered that the momentum (q)-dependent effective charges, introduced in our reference paper (Nature 573, 247 (2019) to measure the phonon oscillator strength, also describe (at finite but small q) the electron-phonon interaction, the LO-TO splitting and the IR reflectivity, not only in insulators, but also in doped semiconductors, metals and superconductors [2-4]. These approaches have also been used to describe the phonon EELS signal and the LO-TO splitting in few-layer h-BN flakes, as measured, by the partners [to be published]. We further developed non-perturbative techniques to describe phonons and their spectroscopic signatures [5], and their thermal transport properties [6] in extreme anharmonic systems. For the spectroscopic properties they used a new resonant Raman spectroscopy with IR light to pinpoint a strong enhancement of the electron-phonon coupling and of the Kohn anomaly in graphene at the K-point that we plan to study with MORE-TEM [7]. At the same time they studied the role of infrared active phonons in STO to control optical nonlinearities when driven by strong THz pulses [8,9], highlighting possible anomalies connected to the anharmonic effects and dynamical effective charges. For what concerns plasmonic modes they described [10-13] the hybrid plasma-polariton mode in (single and bi-) layered superconductors in the full q range. Experimentally, we also worked on producing 1D samples for MORE-TEM understanding and optimising the growth of confined carbyne using 13C isotope labelling [14], as well as measuring on the Japanese reference systems and analysing new experiments in comparison to contemporary theory. Examples cover some first experiments regarding the momentum resolved excitonic effect on 2D layered materials like PdSe2[15]. The specimen preparation techniques for novel low-D structures also advanced. For example, new intercalation structures of metal chlorides in BLG were investigated by EELS and STEM imaging [16]. Dark-field EELS for vibrational spectroscopy has turned out as useful to map the isotope at high spatial resolution [17]. Finally, new EELS experiments on freestanding graphene at the utmost available energy and q resolution revealed, for the first time, the excitation gap and the modelisation of q dependent EELS of electronic excitation revealed the importance of excitonic effects (electron-hole attraction) [18].
[1] F. Börrnert, et al. Ultramicroscopy (accepted) (2023).
[2] F. Macheda, et al. PRB 107, 094308 (2023); arXiv:2212.12237
[3] G. Marchese, et al, Nature Phys., accepted (2023); arXiv:2303.00741
[4] F. Macheda, P. Barone, and F. Mauri, PRL 129, 185902 (2022); arXiv:2202.02835.
[5] A. Siciliano, et al., PRB 107, 174307 (2023); arXiv:2301.08628
[6] G. Caldarelli, et al., PRB 106, 024312 (2022); arXiv:2202.02246
[7] T. Venanzi, et al., PRL, accepted (2023); arXiv:2212.01342
[8] M. Basini, et al., submitted (2022), arXiv:2210.14053
[9] M. Basini, et al., submitted (2022), arXiv:2210.01690
[10] J. P. Nery, F. Mauri, PRB 105, 245120 (2022); arXiv:2203.11289
[11] S. Mallik et al., Nat. Com. 13, 4625 (2022)
[12] F. Gabriele, C. Castellani, L. Benfatto, PR Res, 4, 023112 (2022); arXiv:2110.06772
[13] N. Sellati, et al., submitted (2023), arXiv:2304.14816
[14] W. Cui et al. Adv. Funct. Mat., 32, 2206429 (2022)
[15] J. Hong et al. ACSNano 16, 12328 (2022)
[16] Y.C. Lin et al., Nanolett. 21, 10386 (2021)
[17] R. Senga et al., Nature 603, 68 (2022)
[18] A. Guandalini et al., submitted (2023), arXiv:2302.06367
[1] F. Börrnert, et al. Ultramicroscopy (accepted) (2023).
[2] F. Macheda, et al. PRB 107, 094308 (2023); arXiv:2212.12237
[3] G. Marchese, et al, Nature Phys., accepted (2023); arXiv:2303.00741
[4] F. Macheda, P. Barone, and F. Mauri, PRL 129, 185902 (2022); arXiv:2202.02835.
[5] A. Siciliano, et al., PRB 107, 174307 (2023); arXiv:2301.08628
[6] G. Caldarelli, et al., PRB 106, 024312 (2022); arXiv:2202.02246
[7] T. Venanzi, et al., PRL, accepted (2023); arXiv:2212.01342
[8] M. Basini, et al., submitted (2022), arXiv:2210.14053
[9] M. Basini, et al., submitted (2022), arXiv:2210.01690
[10] J. P. Nery, F. Mauri, PRB 105, 245120 (2022); arXiv:2203.11289
[11] S. Mallik et al., Nat. Com. 13, 4625 (2022)
[12] F. Gabriele, C. Castellani, L. Benfatto, PR Res, 4, 023112 (2022); arXiv:2110.06772
[13] N. Sellati, et al., submitted (2023), arXiv:2304.14816
[14] W. Cui et al. Adv. Funct. Mat., 32, 2206429 (2022)
[15] J. Hong et al. ACSNano 16, 12328 (2022)
[16] Y.C. Lin et al., Nanolett. 21, 10386 (2021)
[17] R. Senga et al., Nature 603, 68 (2022)
[18] A. Guandalini et al., submitted (2023), arXiv:2302.06367
As a technological breakthrough shown in Ref [1] and Figure 1 CEOS will generate a new device which will be open for almost the whole community due to the goal to develop a retrofit-able monochromator. This importance is not only for us, it is much more for the whole electron microscopy community because there is huge demand on such a device and the existing monochromators can only be attained if one accepts the microscope which is coming with the monochromator. Our design is defined in such a way that it can be used for various types of electron microscopes and it will, in principle, be independent of the vendor of the microscope.
As highlighted in Ref. [17] using momentum integrated EELS a breakthrough in the ability to distinguish different carbon isotopes in the TEM on the single atom level was proven. It shows the first study how to use the changes in the phonon DOS due to the different masses of the individual isotopes to distinguish them on the single atom level. This is impossible from the image contrast alone. This sensitivity to distinguish atomically resolved between different carbon isotopes published in Nature is a breakthrough which only became available by our reference study in Nature (R. Senga, K. Suenaga, P. Barone, S. Morishita, F. Mauri, T. Pichler, Position and momentum mapping of vibrations in graphene nanostructures, Nature 573 (2019) 247). The same holds for the highlight in Ref. 3. The theory partner introduced the concept of atomic momentum (q) dependent effective charges ZI(q), a vector quantity associated to each atom I of the unit cell, to describe the phonon cross-section measured by EELS. Interestingly, we discovered that in presence of a strong electron scattering (as, e.g. in a high temperature superconductor) Z(q) can be used to also describe the phonon peaks in optical reflectivity data in the far-IR. In the accepted Nature Phys. in Ref. 3 we used this concept to extend the definition of Born effective charges, normally used in insulators, to super and bad conducting metals and to simulate the far-IR reflectivity spectra of the extremely high-temperature superconductor, H3S, both in its normal and superconducting phase. This is a breakthrough regarding IR mode detection in metals.
For momentum resolved EELS at high energy resolution the breakthrough in the optical range the highlights in Ref. 15 and 18 represent a breakthrough regarding the experimental detection and concomitant theoretical description. The paper submitted to PRL provides the first combined experimental and theoretical study on the excitation gap opening of graphene. This is a breakthrough as it is the first experiment allowing access to the Fermi velocity in freestanding graphene. This enabled us to disentangle the quasielastic scattering from the excitation gap of Dirac electrons of freestanding graphene, even close to the optical limit. Combining this possibility with first-principles calculations, we show the importance of many-body effects on electronic excitations. Quasi-particle corrections and excitonic effects are addressed within the GW approximation and Bethe-Salpeter equation, respectively. Both effects are essential in the description of the EEL spectra to obtain a quantitative agreement with experiments, with the position, dispersion, and shape of both the onset and the π plasmon being significantly affected by excitonic effects. In semiconductors such as 2D layered PdSe2 which has a layer dependent metal insulator transition published in ACSNano we have proven that such high energy and momentum resolutions are also crucial to disentangle different quasiparticle excitations. i.e. how to disentangle plasmonic and excitonic response and the layer dependent metal insulator transition. This is a breakthrough regarding the ability to distinguish the origin of these quasiparticle excitations.
All these 17 publications and 12 highlights in the first two years show the pathway to achieve the above mentioned final goal of the project to develop a revolutionary new research instrument as table top synchrotron combining the utmost combined energy resolution with the concomitant utmost either momentum or spatial resolution at variable temperature. Mapping out the spatial and q-landscape of primary excitations will allow us to gain control on quantum phases, like charge-density waves and superconductivity, to engineer new materials for energy (e.g. batteries), (opto-)electronic devices in (organic) electronics, and to model the physical and chemical properties of natural geological systems. Hence, this will not only enable the analysis of modern advanced materials in unprecedented details but also hugely impact a wide range of applications in physics, chemistry, engineering, as well as in environmental-, geo- & material science.
As highlighted in Ref. [17] using momentum integrated EELS a breakthrough in the ability to distinguish different carbon isotopes in the TEM on the single atom level was proven. It shows the first study how to use the changes in the phonon DOS due to the different masses of the individual isotopes to distinguish them on the single atom level. This is impossible from the image contrast alone. This sensitivity to distinguish atomically resolved between different carbon isotopes published in Nature is a breakthrough which only became available by our reference study in Nature (R. Senga, K. Suenaga, P. Barone, S. Morishita, F. Mauri, T. Pichler, Position and momentum mapping of vibrations in graphene nanostructures, Nature 573 (2019) 247). The same holds for the highlight in Ref. 3. The theory partner introduced the concept of atomic momentum (q) dependent effective charges ZI(q), a vector quantity associated to each atom I of the unit cell, to describe the phonon cross-section measured by EELS. Interestingly, we discovered that in presence of a strong electron scattering (as, e.g. in a high temperature superconductor) Z(q) can be used to also describe the phonon peaks in optical reflectivity data in the far-IR. In the accepted Nature Phys. in Ref. 3 we used this concept to extend the definition of Born effective charges, normally used in insulators, to super and bad conducting metals and to simulate the far-IR reflectivity spectra of the extremely high-temperature superconductor, H3S, both in its normal and superconducting phase. This is a breakthrough regarding IR mode detection in metals.
For momentum resolved EELS at high energy resolution the breakthrough in the optical range the highlights in Ref. 15 and 18 represent a breakthrough regarding the experimental detection and concomitant theoretical description. The paper submitted to PRL provides the first combined experimental and theoretical study on the excitation gap opening of graphene. This is a breakthrough as it is the first experiment allowing access to the Fermi velocity in freestanding graphene. This enabled us to disentangle the quasielastic scattering from the excitation gap of Dirac electrons of freestanding graphene, even close to the optical limit. Combining this possibility with first-principles calculations, we show the importance of many-body effects on electronic excitations. Quasi-particle corrections and excitonic effects are addressed within the GW approximation and Bethe-Salpeter equation, respectively. Both effects are essential in the description of the EEL spectra to obtain a quantitative agreement with experiments, with the position, dispersion, and shape of both the onset and the π plasmon being significantly affected by excitonic effects. In semiconductors such as 2D layered PdSe2 which has a layer dependent metal insulator transition published in ACSNano we have proven that such high energy and momentum resolutions are also crucial to disentangle different quasiparticle excitations. i.e. how to disentangle plasmonic and excitonic response and the layer dependent metal insulator transition. This is a breakthrough regarding the ability to distinguish the origin of these quasiparticle excitations.
All these 17 publications and 12 highlights in the first two years show the pathway to achieve the above mentioned final goal of the project to develop a revolutionary new research instrument as table top synchrotron combining the utmost combined energy resolution with the concomitant utmost either momentum or spatial resolution at variable temperature. Mapping out the spatial and q-landscape of primary excitations will allow us to gain control on quantum phases, like charge-density waves and superconductivity, to engineer new materials for energy (e.g. batteries), (opto-)electronic devices in (organic) electronics, and to model the physical and chemical properties of natural geological systems. Hence, this will not only enable the analysis of modern advanced materials in unprecedented details but also hugely impact a wide range of applications in physics, chemistry, engineering, as well as in environmental-, geo- & material science.